This Thesis presents the results of phase behavior calculations and simulation of asphaltene precipitation, flocculation, and deposition in five Middle-Eastern wells from different fields, based on a reliable experimental data provided for this purpose. The asphaltene precipitation, flocculation, and deposition have been simulated throughout the primary (pressure depletion), secondary (Waterflooding) and tertiary recovery (CO₂ injection) stages. Asphaltene precipitation becomes a serious problem especially when it causes plugging of the formation, wellbore, or production facilities, which will significantly affect the productivity and final recovery of the area. To help preventing asphaltene precipitation a bottomhole pressure higher than the asphaltene onset pressure (AOP) has been applied. Also, water and CO₂ injection has provided enough support for pressure maintenance, which helps in preventing asphaltene. Several scenarios were tested to investigate and identify the cases with lowest asphaltene precipitation and higher recovery. It has been considered obligatory to have a representative numerical simulation model that can predict the phase behavior of asphaltene precipitation, flocculation, and deposition accurately. The first part of this thesis includes a comprehensive literature review of asphaltene precipitation flocculation, and deposition that include asphaltene structure, models and prevention techniques. The second part of the thesis includes a detailed study of modeling asphaltene precipitation phase behavior utilizing experimental and real field data obtained from five Middle-Eastern wells from different fields. Experimental data include measurements of asphaltene onset pressure (AOP), saturation pressure, and PVT data. Asphaltene precipitation was modeled by using WinProp (a phase behavior utility from CMG) which uses Nghiem solid model. Saturation pressures, PVT, and AOP data were used to match Peng-Robinson EOS and the precipitation model was matched by the experimental data of AOP. The third part of the thesis includes a one-dimensional simulation comparison study of asphaltene precipitation between three different compositional simulators; UTCOMP, ECLIPSE and CMG/GEM. The last part of the thesis includes a full field scale study based on a heterogeneous three-dimensional cartesian single-well model. The objective of this study was to assess the effect of asphaltene precipitation, flocculation, and deposition in the well productivity and the economic impacts related to it. Different production practices were applied to define the most appropriate and efficient production strategy. This study includes a discussion and comparison of production rates with and without asphaltene precipitation, flocculation, and deposition and a comparison of asphaltene precipitation, flocculation, and deposition at different times using different bottomhole and production rate constraints. Several cases (i.e., WAG cycles, completion, target layers of injection, etc.) will be tested to come up with the optimum completion and operating strategy in the presences asphaltene. Despite the work devoted to understanding this subject, asphaltene still represents a challenging and unresolved problem. This thesis will help bridge the gap of this limited understanding in the field of asphaltene. / text

Multiple hydrocarbon phases are observed during miscible gas floods. The possible phases that result from a gas flood include a vapor phase, an oleic phase, a solvent-rich phase, a solid phase, and an aqueous phase. The solid phase primarily consists of aggregated asphaltene particles. Asphaltenes can block pore throats or change the formation wettability, and thereby reduce the hydrocarbon mobility. The dissolution of injected gas into the aqueous phase can also affect the gas flooding recovery because it reduces the amount of gas available to contact oil. This is more important in CO₂ flooding as the solubility of CO₂ in brine is much higher than hydrocarbons. In this research, we developed efficient and fast multi-phase equilibrium calculation algorithms to model phase behavior of asphaltenes and the aqueous phase in the compositional simulation of gas floods. The PC-SAFT equation of state is implemented in the UTCOMP simulator to model asphaltene precipitation. The additional computational time of PC-SAFT is substantially decreased by improving the root finding algorithm and calculating the derivatives analytically. A deposition and wettability alteration model is then integrated with the thermodynamic model to simulate dynamics of precipitated asphaltenes. Asphaltene deposition is shown to occur with pressure depletion around the production well and/or with gas injection in the reservoir domain that is swept by injected gas. It is observed that the profile of the damaged area by asphaltene deposition depends on the reservoir fluid. A general strategy is proposed to model the phase behavior of CO₂/hydrocarbon/water systems where four equilibrium phases exist. The developed four-phase reduced flash algorithm is used to investigate the effect of introducing water on the phase behavior of CO₂/hydrocarbon mixtures. The results show changes in the phase splits and saturation pressures by adding water to these CO₂/hydrocarbon systems. We used a reduced flash approach to reduce the additional computational time of the four-phase flash calculations,. The results show a significant speed-up in flash calculations using the reduced method. The computational advantage of the reduced method increases rapidly with the number of phases and components. We also decreased the computational time of the equilibrium calculations in UTCOMP by changing the sequential steps in the flash calculation where it checks the previous time-step results as the initial guess for the current time-step. The improved algorithm can skip a large number of flash calculation and stability analyses without loss of accuracy. / text

Asphaltene precipitation, flocculation, and deposition in the reservoir and producing wells cause serious damages to the production equipment and possible failure to develop the reservoirs. From the field production prospective, predicting asphaltene precipitation, flocculation, and deposition in the reservoir and wellbore may avoid high expenditures associated with the reservoir remediation, well intervention techniques, and field production interruption. Since asphaltene precipitation, flocculation, and deposition strongly depend on the pressure, temperature, and composition variations (e.g. phase instability due to CO2 injection), it is important to have a model that can track the asphaltene behavior during the entire production system from the injection well to the production well, which is absent in the literature. Due to economic concerns for asphaltene related problems, companies spend a lot of money to design their own asphaltene inhibition and remediation procedures. However, due to the complexity and the lack of knowledge on the asphaltene problems, these asphaltene inhibition and remediation programs are not always successful. Near-wellbore asphaltene inhibition and remediation techniques can be divided into two categories: changing operating conditions, and chemical treatment of the reservoir. Although, the field applications of these procedures are discussed in the literature, a dynamic model that can handle asphaltene inhibition and remediation in the reservoir is missing. In this dissertation, a comprehensive non-isothermal compositional reservoir simulator with the capability of modeling near-wellbore asphaltene inhibition and remediation is developed to address the effect of asphaltene deposition on the reservoir performance. This simulator has many additional features compared to the available asphaltene reservoir simulators. We are able to model asphaltene behavior during primary, secondary, and EOR stages. A new approach is presented to model asphaltene precipitation and flocculation. Adsorption, entrainment, and pore-throat plugging are considered as the main mechanisms of the asphaltene deposition. Moreover, we consider porosity, absolute permeability, and oil viscosity reductions due to asphaltene. It is well known that the asphaltene deposition on the rock surface changes the wettability of the rock towards oil-wet condition. Although many experiments in the literature have been conducted to understand the physics underlying wettability alteration due to asphaltene deposition, a comprehensive mathematical model describing this phenomenon is absent. Based on the available experimental data, a wettability alteration model due to asphaltene deposition is proposed and implemented into the simulator. Furthermore, the reservoir simulator is coupled to a wellbore simulator to model asphaltene deposition in the entire production system, from the injection well to the production well. The coupled reservoir/wellbore model can be used to track asphaltene deposition, to diagnose the potential of asphaltene problems in the wellbore and reservoir, and to find the optimum operating conditions of the well that minimizes asphaltene problems. In addition, the simulator is capable of modeling near-wellbore asphaltene remediation using chemical treatment. Based on the mechanisms of the asphaltene-dispersant interactions, a dynamic modeling approach for the near-wellbore asphaltene chemical treatments is proposed and implemented in the simulator. Using the dynamic asphaltene remediation model, we can optimize the asphaltene treatment plan to reduce asphaltene related problems in a field. The results of our simulations show that asphaltene precipitation, flocculation, and deposition in the reservoir and wellbore are dynamic processes. Many parameters, such as oil velocity, wettability alteration, pressure, temperature, and composition variations influence the trend of these processes. In the simulation test cases, we observe that asphaltene precipitation, flocculation, and deposition can occur in primary production, secondary production, or EOR stages. In addition, our results show that the wettability alteration has the major effect on the performance of the reservoir, comparing to the permeability reduction. During CO2 flooding, asphaltene precipitation occurs mostly at the front, and asphaltene deposition is at its maximum close to the reservoir boundaries where the front velocity is at its minimum. In addition, the results of the coupled reservoir/wellbore simulator show that the behavior of asphaltene in the wellbore and reservoir are fully coupled with each other. Therefore, a standalone reservoir or wellbore simulator is not able to predict the asphaltene behavior properly in the entire system. Finally, we show that the efficiency of an asphaltene chemical treatment plan depends on the type of dispersant, amount of dispersant, soaking time, number of treatment jobs, and the time period between two treatment jobs. / text